In an impact tool, a rotation striking mechanism is driven by a motor as a driving source to provide rotation and striking to an anvil, thereby intermittently transmitting rotation striking power to a tip tool for performing operation, such as screwing. As a motor, a brushless DC motor is widely used. The brushless DC motor is, for example, a DC (direct current) motor with no brush (brush for commutation). Coils (windings) are used on the stator side, magnets (permanent magnets) are used on the rotor side, and a rotor is rotated as the electric power driven by an inverter circuit is sequentially applied to predetermined coils. The inverter circuit is constructed using an FET (field effect transistor), and a high-capacity output transistor such as an IGBT (insulated gate bipolar transistor), and is driven by a large current. The brushless DC motor has excellent torque characteristics as compared with a DC motor with a brush, and is able to fasten a screw, a bolt, etc. to a base member with a stronger force.
JP-2009-072888-A discloses an impact tool using the brushless DC motor. In JP-2009-072888-A, the impact tool has a continuous rotation type impact mechanism. When torque is given to a spindle via a power transmission mechanism (speed-reduction mechanism), a hammer which movably engages in the direction of a rotary shaft of the spindle rotates, and an anvil which abuts on the hammer is rotated. The hammer and the anvil have two hammer convex portions (striking portions) which are respectively arranged symmetrically to each other at two places on a rotation plane, these convex portions are at positions where the gears mesh with each other in a rotation direction, and rotation striking power is transmitted by meshing between the convex portions. The hammer is made axially slidable with respect to the spindle in a ring region surrounding the spindle, and an inner peripheral surface of the hammer includes an inverted V-shaped (substantially triangular) cam groove. A V-shaped cam groove is axially provided in an outer peripheral surface of the spindle, and the hammer rotates via balls (steel balls) inserted between the cam groove and the inner peripheral cam groove of the hammer.
In the conventional power transmission mechanism, the spindle and the hammer are held via the balls arranged in the cam groove, and the hammer is constructed so as to be able to retreat axially rearward with respect to the spindle by the spring arranged at the rear end thereof. As a result, the number of parts of the spindle and the hammer increases, high attaching accuracy between the spindle and the hammer is required, thereby increasing the manufacturing cost.
Meanwhile, in the impact tool of the conventional technique, in order to perform a control so as not to operate the impact mechanism (that is, in order that striking does not occur), for example, a mechanism for controlling a retreat operation of the hammer is required. The impact tool of JP-2009-072888-A cannot be used in a so-called drill mode. Further, even if a drill mode is realized (even if a retreat operation of the hammer is controlled), in order to realize even the clutch operation of interrupting power transmission when a given fastening torque is achieved, it is necessary to provide a clutch mechanism separately, and realizing the drill mode and the drill mode with a clutch in the impact tool leads to cost increase.
Further, in JP-2009-072888-A, the driving electric power to be supplied to the motor is constant irrespective of the load state of a tip tool during the striking by the hammer. Accordingly, striking is performed with a high fastening torque even in the state of light load. As a result, excessive electric power is supplied to the motor, and useless power consumption occurs. And, a so-called coming-out phenomenon occurs where a screw advances excessively during screwing as striking is performed with a high fastening torque, and the tip tool is separated from a screw head.
A conventional power tool mainly has a motor, a hammer rotationally driven by the motor, and an anvil to which torque is imparted through collision with the hammer (for example, refer to JP-2008-307664-A). As the torque transmitted to the anvil is imparted to a tip tool, the fastening work of a screw or the like is performed. In the power tool, as an engaging projection provided on the hammer and an engaged projection provided on the anvil collide with each other, torque is imparted to the anvil, and the torque is transmitted to the tip tool.
However, in a conventional power tool, the engaging projection collides in a state where the speed has been increased by the motor. For this reason, a problem occurs in that the impact of the collision between the engaging projection and the engaged projection becomes large, and fastening torque increases. Particularly when the increased fastening of fastening a screw or the like which has been fastened again is performed, since the fastening torque is already imparted to the screw, the torque may become excessively large due to the impact of the collision between the engaging projection and the engaged projection. Thus, the object of the invention is to provide a power tool capable of preventing torque exceeding a target torque from being supplied to a fastener.
In conventional power tools, there is a power tool in which it is determined that a predetermined torque has been obtained when a predetermined current value is reached, and supply of electric power to a motor is automatically stopped. Although such products have been sold, the stopping of the supply of electric power to the motor occurs, for example, when a power cord has been pulled in a case where the power cord is used, or when the remaining battery level of the charging battery has been reduced in a case where the charging battery is used, other than when the predetermined torques are reached. For this reason, when a predetermined torque is reached, it is necessary to make the event easily understood by a worker.
However, in the conventional power tool, the operation continues unless the worker takes his/her finger off the trigger. Therefore, useless power consumption occurs, and the temperature of the motor also rises. Especially when compared with normal operation (the motor rotates continuously in one direction), the normal rotation and stop of the motor are repeated in a ratcheting operation mode. Therefore, the power consumption and the temperature rise of the battery are conspicuous. Thus, an object of the invention is to provide a power tool capable of, when a predetermined torque is reached, making the event easily understood. Another object of the invention is to provide a power tool capable of making it hard to uselessly consume electric power and obtaining high-precision torque, when making the event easily understood.
A worker is able to make a screw or the like and a tip tool of a power tool fit each other, and to depress a trigger, thereby performing fastening work of a fastener. When a worker fastens a bolt to a member to be worked in which a lead is formed, since resistance is small, a current value shifts to a low value, and at a moment when a bolt is seated, the current value abruptly rises and exceeds a threshold value at once.
In such a case, even if the motor is stopped by turning OFF the trigger, a stop operation is delayed due to the inertia of the motor, and the bolt is fastened with a value which is equal to or more than a desired torque value. Thus, the object of the invention is to provide a power tool capable of supplying a precise target torque.
In a conventional power tool, a structure in which an anvil is struck in a given direction by a hammer which rotates in the given direction is known (for example, refer to JP-2008-307664-A).
However, in the conventional power tool, when a trigger is depressed in a state where the fitting between a screw and a tip tool is in an imperfect state at the time of start-up, the fitting between the screw and the tip tool may be released (coming-out), and the head of the screw may be damaged. Thus, the object of the invention is to provide a power tool capable of preventing the coming-out of a tip tool from a fastener.
In a conventional power tool, a motor is controlled regardless of the temperature of a built-in object of the housing (for example, refer to JP-2010-058186-A).
In the conventional power tool, the motor is driven without taking generation of heat of the built-in object of the housing into consideration. For this reason, for example, if the ambient temperature is low, there is a case where the viscosity of grease of a gear mechanism changes, the grease hardens, and the current value of the motor rises. For this reason, it is necessary to alter the electric power to be supplied to the motor depending on whether the ambient temperature is low, or the ambient temperature is high.
Additionally, if the ambient temperature is high, switching elements for supplying electric power to coils of the motor may be damaged as the switching elements generate heat. For this reason, it is necessary to prevent the temperature of the switching elements from becoming too high. The object of the invention is to provide a power tool adapted to change the control method of a motor according to the temperature of a built-in object of the housing.
In a conventional power tool, a structure in which an anvil is struck in a given direction by a hammer which rotates in the given direction is known (for example, refer to JP-2008-307664-A).
Meanwhile, the applicant of the invention has newly developed an electronic pulse driver constructed to normally rotate and reversely rotate the hammer, thereby striking the anvil. However, in the newly developed electronic pulse driver, the fitting between a screw or the like and a tip tool may be released (come-out), and the head of the screw may be damaged. Moreover, a force in the direction reverse to the rotational direction is generated in the power tool by the reaction caused by the operation after seating, and the worker experiences discomport. Thus, the object of the invention is to provide a power tool capable of reducing the reaction force from a member to be worked.
A conventional power tool is adapted to rotate a fastener by an output shaft. The control of a motor is the same even when a plurality of fasteners is used (for example, refer to JP-2008-307664-A).
However, in the conventional power tool, it is difficult to perform fastening according to the fasteners used. Particularly when the fastening work of a wood screw is performed, the wood screw needs to perform fastening even after seating, and a control which gives a high torque to a tip tool is required. Moreover, when the fastening work of a bolt is performed, further fastening cannot be performed after seating. Therefore, when the normal rotation time of pulses is long, a force reverse to a rotational direction is generated in an impact driver by the reaction of the bolt, and the worker experiences discomfort. Then, the object of the invention is to provide a power tool capable of discriminating a fastener. By such a power tool, the control of a motor can be varied in a case where fasteners are different.
In an electric impact driver which is an example of a conventional power tool, a motor is rotated in a given rotational direction to rotate a hammer in the given direction and to rotate an anvil in a given direction (for example, refer to JP-2008-307664-A).
In the conventional power tool, the motor is controlled regardless of the temperature of a built-in object of the housing. Additionally, as an embodiment of the invention, in a power tool which normally rotates or reversely rotates the motor, generation of heat by the motor increases. As such, in the power tool in which generation of heat of the motor becomes large, the temperature of the motor may rise excessively in a case where the motor is controlled regardless of the temperature of the motor. The object of the invention is to provide a power tool capable of controlling a motor according to the temperature of a built-in object of the housing. By such a power tool, the temperature of the built-in object of the housing rarely rises excessively.
In a conventional power tool, a structure in which an anvil is struck in a given direction by a hammer which rotates in the given direction is known (for example, refer to JP-2008-307664-A).
Meanwhile, the applicant of the invention has newly developed an electronic pulse driver constructed to normally rotate and reversely rotate the hammer, thereby striking the anvil. However, in the newly developed electronic pulse driver, if the normal rotation time is long during high-load work, the reaction of the impact driver also increases, and the worker experiences increasing discomfort. Thus, the object of the invention is to provide a power tool which is comfortable to use.